Metal staples to prevent interlayer delamination

ABSTRACT

The present invention provides in one embodiment thereof an integrated circuit (IC) that includes silicon substrate. The integrated circuit includes a plurality of dielectric and metal layers formed upon the silicon substrate. The plurality of dielectric and metal layers form a die active area. The metal have formed therein a first guard wall surrounding the die active area. The metal layers further have formed therein a second segmented guard wall. The segmented guard wall surrounds and staples the plurality of metal layers. The IC also includes a passivation layer adhering to the first and the segmented guard walls.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to the field of semiconductor fabrication.More specifically, the present invention relates to integrated circuitswith structures that reduce or prevent damages to the integratedcircuit.

(2) Background Information

Presently, semiconductor integrated circuits are manufactured bydeposition and etch of a number of layers upon a silicon (Si) wafer.Device regions are formed within the Si wafer and then layers ofconductive and non conductive material are formed over the deviceregions. These layers are then masked and etched to form semiconductordevices which are then connected by the use of conductive layers. Theconductive layers typically include metal layers which are deposited,masked and etched to form interconnects. Subsequent layers are formed soas to define additional devices and interconnects. A top dielectriclayer (hereinafter referred to as "passivation layer") is typicallydeposited over a top metal layer (hereinafter referred to as "terminalmetal layer" or "TML") to planarize, insulate, prevent moisturepenetration, thin film cracking, and other types of mechanical andchemical damages which may occur during assembly, packaging andoperation of the individual integrated circuit die on the wafer.

FIG. 1 shows a cross-sectional view through a semiconductor wafer 100.Semiconductor wafer 100 includes a silicon substrate 101 that hasseveral dielectric layers 102, 103 and 104 formed thereupon by processesthat are well-known in the art. The figure also shows three metal layersthat have been deposited, masked, and etched to form metal layers 105,106, and 107. Metal layers 105-107 overlie device regions to connect thevarious devices and the subsequently deposited metal layers. A topdielectric layer 111 (passivation layer) is then formed over theterminal metal layer 105 to planarize, insulate the electrical devicesand interconnects, to prevent leakage of electrical current through thispassivation layer, etc. The passivation layer 111 may include a hardpassivation layer 113 typically made of silicon nitride (SiN) and a softpassivation layer typically made of polyimide 115. The polyimide layercovers the SiN layer. The soft passivation layer is deposited by PlasmaEnhanced Chemical Vapor Deposition or other typically known passivationlayer deposition processes. The layer of silicon nitride is then coveredby polyimide or another type of soft passivation layer.

FIG. 2(a) illustrates a cross-section through the semiconductor wafer ofFIG. 1 where the soft passivation layer 115 is partly delaminated fromthe hard passivation layer 113. The delamination typically allows forpenetration of moisture and other impurities to penetrate in thesemiconductor wafer. One reason for the passivation layer's delaminationis that the die is assembled into a plastic package which is moreconducive to propagation of external forces within the package and tothe die. The passivation layer, may also delaminate, when the die andthe passivation layer are subjected to pressure pot testing (steam at apressure greater than atmospheric pressure). One theory explaining thistype of delamination is that steam dissolves or weakens the bonds withinthe passivation layer causing the passivation layer itself todelaminate.

Delamination is more likely to occur at the interface between thepassivation layer 111 and the terminal metal layer 105. Delaminationtypically starts at the edge of the die and propagates towards thecenter of the die. If the delamination reaches an electricalinterconnect, the forces within the die, that cause the delamination,are applied to the electrical interconnect causing the electricalinterconnect to rip apart at weak points thereof.

FIG. 2(b) illustrates another cross section of the semiconductor waferof FIG. 1 where the polyimide layer 115 delaminates together with thesilicon nitride layer 113.

FIG. 2(c) illustrates a cross section of the semiconductor wafer of FIG.1 where the terminal metal layer 105 and the passivation layer 111,including the silicon nitride layer 113 and the polyimide layer 115,delaminate from dielectric layer 104 as a result of external forcesapplied to the semiconductor wafer of FIG. 1.

What is needed is to provide a silicon wafer with reduced delaminationof the passivation layer from the terminal metal layer, reduceddelamination of the terminal metal layer and the passivation layer froma dielectric layer, and reduced delamination of the soft passivationlayer from the hard passivation layer.

FIG. 3 illustrates a cross sectional view of a semiconductor wafer thathas two chips 302 and 304 formed therein. These chips are separated by asawing process. The sawing process, in this example, cuts the siliconsubstrate and all of the overlying layers to form the two chips 302 and304.

FIG. 4 illustrates a top view of four dies 410 of a wafer separatedtherebetween by cuts resulting from a sawing process. Each die 410 hasan active area 401 demarcated by dotted edge 421. Each die alsoincludes, at a periphery thereof, a guard ring 412 surrounding the diearea. Modern silicon wafers are typically provided, for each die, with aguard ring or guard wall that surrounds a die active area and thatprotects the die active area from damages. The damages include invasionby foreign impurities, such as sodium and magnesium that are existent inthe environment, certain mechanical damages, including microcracks,produced by the wafer saw process and that propagate into an active diearea of the chip, etc.

Saw cuts through the silicon wafer are typically not straight but ratherwavy as shown in the figure (vertical cut 411 and horizontal cut 413).Also, the space between the dies through which the cut is made, isrelatively small to provide more chips per wafer (package integration).Therefore, often, the saw cut may be made partially through the guardring 412 as shown in the figure at 408 and 409. Cuts through the guardring may cause failure of the guard ring to adequately protect the dieactive area and damages to the die active area 401 may ensue. Moreover,saw damage combined with reliability testing, (steam, temperaturecycling, etc.) tend to cause the multi-layer structures of the siliconwafer to delaminate. It is desirable to provide a wafer that reduces thepossibility of sawing cuts through the guard wall. It is also desirableto provide a way of preventing interlayer delamination.

SUMMARY OF THE INVENTION

The present invention provides in one embodiment thereof an integratedcircuit (IC) that includes silicon substrate. The integrated circuitincludes a plurality of dielectric and metal layers formed upon thesilicon substrate. The plurality of dielectric and metal layers form adie active area. The metal have formed therein a first guard wallsurrounding the die active area. The metal layers further have formedtherein a second segmented guard wall. The segmented guard wallsurrounds and staples the plurality of metal layers. The IC alsoincludes a passivation layer adhering to the first and the segmentedguard walls.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, aspects, and advantages of the present invention willbecome more fully apparent from the following Detailed Description,appended claims, and accompanying drawings in which:

FIG. 1 shows a cross-sectional view through a semiconductor wafer;

FIGS. 2a, 2b, and 2c illustrate cross-sectional views through thesemiconductor wafer of FIG. 1 exhibiting different types of delaminationof a passivation layer and of a terminal metal layer;

FIG. 3 illustrates a cross sectional view through a semiconductor waferthat has a plurality of computer chips formed therein that are separatedby a sawing process;

FIG. 4 illustrates a top view of four dies of a wafer separatedtherebetween by cuts resulting from a sawing process;

FIG. 5 illustrates a top view of an embodiment of an integrated circuitaccording to the present invention;

FIG. 6 illustrates a simplified top and lateral view of an embodiment ofan integrated circuit with locking structures according to the presentinvention;

FIG. 7 shows a cross sectional view through a top part of an integratedcircuit according to the present invention;

FIG. 8 illustrates a top view of a portion of a wafer that includes fouradjacent chips;

FIG. 9 illustrates a top view of an integrated circuit with a pluralityof energy absorbing structures according to the present invention;

FIG. 10 illustrates a cross sectional view through an integrated circuitaccording to the present invention with a stapling structure accordingto the present invention;

FIG. 11 illustrates a top view of an embodiment of an integrated circuitwith one guard ring and a segmented stapling structure according to thepresent invention; and

FIG. 12 illustrates a top view of embodiment of an integrated circuit(IC) with three guard rings according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, numerous specific details are set forth toprovide a thorough understanding of the present invention. However, onehaving ordinary skill in the art should recognize that the invention maybe practiced without these specific details. In some instances,well-known circuits, structures, and techniques have not been shown indetail to avoid obscuring the present invention.

FIG. 5 illustrates a top view of an embodiment of a die (integratedcircuit) 500 according to the present invention. The integrated circuitincludes a silicon substrate (not shown) upon which dielectric and metallayers are formed. The metal layers are interposed between thedielectric layers. A terminal metal layer (TML) 502 is formed upon aterminal dielectric layer 503. Terminal dielectric layer 503 is the mostremote layer of dielectric, in a vertical direction perpendicular to theFigure, from the silicon substrate. TML 502 is the most remote layer ofmetal, in a vertical direction perpendicular to the Figure, from thesilicon substrate.

TML includes a continuous guard ring 504 that surrounds a die activearea 501 of the integrated circuit. The die active area 501 includesactive and passive electrical structures that form electrical circuits.To prevent a passivation layer (not shown) from delaminating from guardring 504, or to prevent the guard ring 504 and the passivation layerfrom delaminating from the terminal dielectric layer 503, the embodimentof the integrated circuit of the present invention described hereinincludes a plurality of metal locking structures 506 formed out of theterminal metal layer 502. The locking structures 506 are metal segmentsmade out of the TML, electrically insulated from the die active area501, formed outside the die active area in the vicinity of edges 575 ofthe IC, and in the vicinity of corners 550 of the IC. The embodiment ofthe present invention described herein includes guard ring 504, whichencloses the die active area 501 and locking structures 506

A passivation layer is formed upon guard ring 504 and the lockingstructures 506. The locking structures 506 provide an increased level ofadherence of the passivation layer to the integrated circuit, i.e., anincreased level of adherence of the passivation layer to the last layerof dielectric 503 and to guard ring 504. Structures 580 placed at thecorners of the die 500, may be used for pattern recognition.

Each locking structure 506 is coupled to a voltage supply such as V_(SS)or V_(CC) to reduce stray charges built up on the locking structures 506thereby minimizing the capacitive impact that may be introduced bylocking structures 506. Note that the present invention is not limitedto an integrated circuit with a guard ring 504. The scope of the presentinvention also covers integrated circuits with no guard ring 504, butwith locking structures 506 formed in the terminal metal layer 502 inthe vicinity of edges 575 of the IC.

FIG. 6 illustrates a simplified top and lateral view, taken through lineA-A' of FIG. 5, of an embodiment of an integrated circuit (IC) 600 withlocking structures 506 according to the present invention. Integratedcircuit 600 includes metal layers (M1, M2, M3, M4, M5) interposedbetween layers of dielectric (not shown). M5 is a terminal metal layer(TML) 502 and includes a guard ring 504 formed out of TML layer 502. Aguard wall 508, including guard ring 504, surrounds die active area 501.Note that the present invention also applies to an IC that only has onelayer of metal and one layer of dielectric.

The guard wall 508 is "carved out" of the terminal layer (M5) and of therest of the metal layers (M4, M3, M2, M1) of the integrated circuit 600.A plurality of locking structures 506 are formed out of the TML 502 toincrease a level of adherence of the passivation layer (not shown). Eachlocking structure 506 has a surface (adhering surface) that includes twolateral surfaces 511 and one top surface 531. Surfaces 531 and 511increase the area of adherence of the IC with a passivation layer. Guardring 504 includes top surface 560, lateral external surface 563 andlateral inner surface 520. Therefore the embodiment of the IC 600according to the present invention, provides extra adhering surfacesoffered by locking structures 506 in addition to the above-mentionedsurfaces of the guard ring. The locking structures 506 do not interfacewith the active area, as they are placed outside the active area and areelectrically insulated.

In the embodiment of the present invention described herein, lockingstructures 506 and guard ring 504 are formed by using processeswell-known in the art such as photolithography, patterning, etching,etc. The locking structures 506 upwardly extend from a top surface ofthe terminal dielectric layer (not shown). It has been found that forbetter performance, a width of the locking structures 506 is larger thanthe space 507 between two consecutive locking structures. A good ratioof width-to-space for locking structures 506 may be 3×1. In oneembodiment according to the present invention, the die has a rectangularshape, the guard ring 504 has a rectangular loop shape, and the lockingstructures 506 include parallelepipedical segments. In one embodiment ofthe present invention, each locking structure is parallel to twoopposing sides 575 of the guard ring 504. The placement of lockingstructures 506 near the corners of the die and close to guard ring 504is strategical, in that typically stress concentration is higher at thecorners and edges of the die due to the lower density of metalstructures per unit of surface. The locking structures need not bedisposed near all corners of the die, but only near those corners of thedie that are more susceptible to damage, such as the corners where thedensity of metal structures per unit of surface is lower.

In the embodiment according to the present invention explained herein,the width 571 of a side of guard ring 504 is larger than width 573 of aside of a guard ring formed in metal layer M₄. In the embodiment of thepresent invention described herein, the width 571 is approximately 6 μm,while width 573 is approximately equal to 4 μm. The widths of the othermetal layers (M₁ -M₃) are equal therebetween and measure approximately 4μms. In some other embodiments according to the present invention, thewidths of guard rings of metal layers M₄, M₃. M₂, and M₁ mayprogressively decrease. By having a wider guard ring 504, adhesionbetween the passivation layer and guard ring 504 is increased. Also, ithas been found that a wider guard ring 504 makes the guard wall 508stronger. In one embodiment according to the present invention, TML ismade of Aluminum/Copper. The guard ring 504 and locking structures 506may have a height 572 of approximately 3 μm. A length of the lockingstructures is in the approximate range of 10 to 20 μm m. A width of thedie 579 may have a size of approximately 1/2 centimeters but such sizeis not limited to 1/2 centimeters.

FIG. 7 shows a cross sectional view through a top part of an integratedcircuit according to the present invention. A terminal metal layer (TML)has a plurality of metal locking structures 506 and a guard ring 504formed therein. These structures are formed by standard processesincluding, patterning the TML, etching the TML, etc. Guard ring 504 isformed towards an edge (side) of the die. A passivation layer includinga hard passivation layer 513 and a soft passivation layer 515 is formedupon and between locking structures 506 and guard ring 504. Thepassivation layer adheres to the top 560 and lateral surfaces 520 and563 of the guard ring 504 and the top 531 and lateral surfaces 511 oflocking structures 506. A width 571 of the guard ring is approximately 6μm. A width 576 of the locking structures has a size in the range ofapproximately 5-15 μm. The metal layer M5 is connected to metal layer M4by way of via 580.

The chips of the wafer are typically separated by a sawing process whichmay cause damage to the guard ring or to the die active areas.Microcracks initiated during the wafer saw process may propagate intothe die active area causing damages to this area. FIG. 8 illustrates atop view of a portion of a wafer 800 that includes four adjacent chips(integrated circuits) 802. Each integrated circuit 802 includes asilicon substrate, a plurality of device layers and metal layers formedupon the silicon substrate, and a first guard wall 811 formed at aperiphery of the metal layers and enclosing a die active area 801.Furthermore, in an embodiment of a wafer with integrated circuitsaccording to the present invention, each IC includes a second guard wall(sacrificial guard wall) 808 formed out of metal layers (M₁, M₂, M₃, M₄,M₅). The sacrificial guard wall 808 encloses the first guard wall 801.The sacrificial guard wall 808 may typically be made of the same metallayers of which the first guard wall 811 is made. The sacrificial guardwall 808 prevents sawing cuts 814 or 815 from producing damages to firstguard wall 811. By having sacrificial guard wall 808 surrounding orenclosing first guard wall 811, the embodiment of the present inventionsubstantially prevents damages to the first guard wall and implicitly tothe die active area 801 had the integrated circuit not included thesacrificial guard wall and the saw directly impacted the first guardwall. The first guard wall 811 is thus "buffered" by sacrificial guardwall 808 that, when intersected by a saw that produces a cuttherethrough, substantially prevents a saw cut from affecting the firstguard wall.

Furthermore, the present invention provides an embodiment of anintegrated circuit (die) 900 with a plurality of energy absorbingstructures shown in FIG. 9. The energy absorbing structures are made outof a terminal metal layer (TML) of the die 900. These energy absorbingstructures are made much in the same way the locking structures aremade. The above-presented discussion with respect to the lockingstructures applies herein. The energy absorbing structures arestrategically placed on a die to absorb saw energy which may damage adie active area. As explained above, it has been found that the cornersof the die and the sides (edges) of the die are more susceptible todamage. One type of energy absorbing structure (shown in a circle at topright corner of the die) includes a plurality of small segments 911 ofmetal that run parallel to two perpendicular sides of the die 921 and923, near the corner of the die. Another type of energy absorbingstructure includes segments 950 placed at the sides of the die andrunning along each edge 921 of the die, from one corner 950 to anotheradjacent corner 951. Different shapes may be conceived for thesesegments. Another type of energy structure is shown in a circle at thebottom left corner of the die. This type of energy absorbing structureincludes two continuous perpendicular segments 906 and 917 joinedtherebetween. Segments 906 and 917 run parallel to sides 929 and 927respectively. The energy absorbing structures may be disposed within aguard ring coinciding with edges 292 to absorb energy resulting from theseparation of the chips from the wafer. A relation between the width ofthe energy absorbing structures and the space therebetween may besimilar with the relation mentioned above, where the ratio of the widthsof the energy absorbing structures to the space therebetween is 3 to 1.

FIG. 10 illustrates a cross sectional view through an integrated circuit(IC) 1000 according to the present invention with a stapling structure1006 configured to reduce or prevent interlayer delamination. Theintegrated circuit according to the present invention includes a guardwall 1002 and a stapling structure 1006 placed between a periphery 1070of the die and guard wall 1002. Stapling structure 1006 holds togetherthe layers of dielectric and metal of IC 1000. Stapling structure 1006is similar to a guard wall, in that it runs through the dielectric andmetal layers of the IC. Stapling structure 1006 of the IC 1000 accordingto the present invention is a segmented structure as shown in FIG. 11.FIG. 10 also illustrates a silicon substrate 1020 upon whichinterspersed metal layers 1008, 1016 and 1018 and dielectric layers1009, 1010, 1012, 1014 and 1022 are formed. Stapling structure 1006 andguard wall 1002 are formed from the metal layers shown in the figure.

FIG. 11 shows a top view of a portion of a die (IC) that has a guardwall 1102 and a segmented stapling structure 1106 (segmented guard wall)routed around guard wall 1102 to prevent interlayer delamination whenmechanical forces are applied to the die. The segmented staplingstructure is advantageous over a continuous structure, as the smallerare the portions of the stapling structure, i.e., segments 1185, thehigher is the resistance to external forces. The segment 1185 shown inthe figure are part of a terminal metal layer (TML) and of the segmentedstapling structure 1106. The segments 1185 enclose a guard ring formedin the TML.

FIG. 12 illustrates a top view of an embodiment of an integrated circuitdie with three guard rings according to the present invention. Aterminal metal layer (TML) formed on a top dielectric layer includes afirst guard ring 1202 formed in the TML. First guard ring 1202 surroundsthe die active area 1201. A second guard ring 1203, formed within theTML, surrounds the first guard ring and protects the first guard ringagainst damages that may occur as a result of sawing, separation of awafer into a plurality of chips, etc. A third guard ring 1204 is formedwithin the TML and surrounds the second guard ring 1203 to protectsecond guard ring 1203 from damages. The third guard ring provides extraprotection, in case the third guard ring was absent and both the secondand first guard rings were damaged. The number of guard ringssurrounding a die active area is not limited to "3". Any number of guardrings may be utilized depending on the desired size of the integratedcircuit.

In the foregoing specification, the invention has been described withreference to specific embodiments thereof. It will however be evidentthat various modifications and changes can be made thereto withoutdeparting from the broader spirit and scope of the invention as setforth in the appended claims. The specification and drawings are,accordingly, to be regarded in an illustrative rather than a restrictivesense. Therefore, the scope of the invention should be limited only bythe appended claims.

What is claimed is:
 1. An integrated circuit (IC) comprising:a siliconsubstrate; a plurality of interspersed dielectric and metal layersformed upon said silicon substrate, said plurality of intersperseddielectric and metal layers forming a die active area, said metal layershaving formed therein a first guard wall surrounding said die activearea, said metal layers further having formed therein a segmented guardwall, surrounding said first guard wall and stapling said plurality ofmetal layers; and a passivation layer adhering to said first and saidsegmented guard wall.
 2. The IC of claim 1 wherein said segmented guardwall includes a plurality of segments surrounding said die active area.3. The IC of claim 1 including a terminal metal layer (TML), said TMLhaving a guard ring formed therein, said guard ring having a rectangularshape.
 4. The IC of claim 3 wherein said TML includes segments that arepart of said segmented guard wall, said segments enclosing said guardring.
 5. The IC of claim 1 wherein the passivation layer includes alayer of silicon nitride and a layer of polyimide.
 6. The IC of claim 4wherein a number of said segments are parallel to a side of arectangular guard ring.
 7. The IC of claim 1 wherein said segmentedguard wall is formed by patterning and etching said terminal metallayer.
 8. The IC of claim 1 wherein said TML layer is made ofaluminum/copper.
 9. The IC of claim 1 wherein said segmented guard wallis made of various layers of conductive material M₁, M₂, M₃, M₄, and M₅.10. The IC of claim 1 wherein said guard ring has a width ofapproximately 6 μm.
 11. A wafer comprising:a plurality of chips, eachchip including:a silicon substrate; a plurality of intersperseddielectric and metal layers formed upon said silicon substrate, saidplurality of interspersed dielectric and metal layers forming a dieactive area, said metal layers having formed therein a first guard wallsurrounding said die active area, said metal layers further havingformed therein a segmented guard wall, surrounding said first guard walland stapling said plurality of metal layers; and a passivation layeradhering to said first and said segmented guard wall.
 12. The wafer ofclaim 11, said segmented guard wall includes a plurality of segmentssurrounding said die active area.
 13. The wafer of claim 11 each chipincluding a terminal metal layer (TML), said TML having a guard ringformed therein, said guard ring having a rectangular shape.
 14. Thewafer of claim 13, said TML includes segments that are part of saidsegmented guard wall, said segments enclosing said guard ring.
 15. Thewafer of claim 11, the passivation layer includes a layer of siliconnitride and a layer of polyamide.
 16. The wafer of claim 14, a number ofsaid segments are parallel to a side of a rectangular guard ring. 17.The wafer of claim 11, said segmented guard wall is formed by patterningand etching said terminal metal layer.
 18. The wafer of claim 11, saidTML layer is made of aluminum/copper.
 19. The wafer of claim 11, saidsegmented guard wall is made of M₁, M₂, M₃, M₄, and M₅.
 20. The wafer ofclaim 11, said guard ring has a width of approximately 6 μm.